Analytical instruments are well known and have been commercially available for many years, in different constructions, for performing a variety of test analyses by various methods.
These instruments, such as clinical hematology lab instruments, typically receive one or a series of test samples, divide each sample into aliquots, and perform one or more tests by combining each aliquot with one or more reagents in a reaction mixture. The reaction mixtures are then analyzed in a known manner. For example, a calorimetric or similar measurement may be made on one reaction mixture while one or more other reaction mixtures may be sent to a particle counting device for a cell count.
One of the disadvantages of such known devices is that they operate with a very limited dynamic range. At low counts, precision suffers and at high counts coincident events (for example, where several cells passing at the same time through the device are counted as one cell or event) limit the range. A variety of methods are implemented in known devices to compensate for these disadvantages.
Known systems typically deliver a fixed volume of a diluted sample solution at a fixed rate for quantitative (i.e., counting) and qualitative (i.e., characterizing) the cells by optical detection means, or magnetic detection means. Techniques involving multiple counts where repetitive delivery of a predetermined volume of diluted sample is performed are sometimes employed to improve low-end precision, but this is done at the expense of sampling throughput.
Conversely, technicians dilute the test samples when cell counts are high, and consequently, the precision for very low cell counts suffers. Moreover, in many cases, the maximum cell capacity is too low for very high cell counts.